Conventionally, energy harvesting techniques and systems are focused on renewable energy such as solar energy, wind energy, and wave action energy. Solar energy is conventionally harvested by arrays of solar cells, such as photovoltaic cells, that convert radiant energy to DC power. Such energy collection is limited in low-light conditions such as at night or even during cloudy or overcast conditions. Conventional solar technologies are also limited with respect to the locations and orientations of installment. For example, conventional photovoltaic cells must be installed such that the light of the sun strikes them at specific angles such that they are receiving relatively direct incident radiation.
Additionally, current photovoltaic cells are relatively large and are limited in where they may be installed. As such, while providing some utility in harvesting energy from the electromagnetic radiation provided by the sun, current solar technologies are not yet developed to take full advantage of the potential electromagnetic energy available. Further, the apparatuses and systems used in capturing and converting solar energy are not particularly amenable to installation in numerous locations or situations.
Moreover, photovoltaic cells are conventionally limited to collection of energy in a very narrow band of light (e.g., approximately 0.8 micrometer to 0.9 micrometer (μm) wavelengths). The spectrum of potentially available electromagnetic energy is much greater than the narrow band in which conventional photovoltaic cells operate. For example, electromagnetic energy provided by the sun falls within the wavelength spectrum of approximately 0.1 μm to approximately 6 μm. Additionally, energy absorbed by the earth and reradiated (e.g., at night) falls within the wavelength spectrum of approximately 3 μm to approximately 70 μm. Current energy harvesting technologies fail to take advantage of such available energy.
Turning to another technology, frequency selective surfaces (FSSs) are used in a wide variety of applications including radomes, dichoric surfaces, circuit analog absorbers, and meanderline polarizers. An FSS is a two-dimensional periodic array of electromagnetic antenna elements. Such antenna elements may be in the form of, for example, conductive dipoles, loop patches, slots or other antenna elements. An FSS structure generally includes a metallic grid of antenna elements deposited on a dielectric substrate. Each of the antenna elements within the grid defines a receiving unit cell.
An electromagnetic wave incident on the FSS structure will pass through, be reflected by, or be absorbed by the FSS structure. This behavior of the FSS structure generally depends on the electromagnetic characteristics of the antenna elements, which can act as small resonance elements. As a result, the FSS structure can be configured to perform as low-pass, high-pass, or dichoric filters. Thus, the antenna elements may be designed with different geometries and different materials to generate different spectral responses.
Conventionally, FSS structures have been successfully designed and implemented for use in radio frequency (RF) and microwave frequency applications. As previously discussed, there is a large amount of renewable electromagnetic radiation available that has been largely untapped as an energy source using currently available techniques. For instance, radiation in the ultraviolet (UV), visible, and infrared (IR) spectra are energy sources that show considerable potential. However, the scaling of existing FSSs or other similar structures for use in harvesting such potential energy sources comes at the cost of reduced gain for given frequencies.
Additionally, scaling FSSs or other transmitting or receptive structures for use with, for example, the IR or near-IR spectra presents numerous challenges due to the fact that materials do not behave in the same manner at the so-called “nano-scale” as they do at scales that enable such structures to operate in, for example, the radio frequency (RF) spectra. For example, materials that behave homogenously at scales associated with the RF spectra often behave inhomogenously at scales associated with the IR or near-IR spectra.
There remains a desire in the art to improve upon existing technologies and to provide methods, structures and systems associated with harvesting energy including structures, methods and systems that provide access to greater bands of the electromagnetic spectrum and, thus greater access to available, yet-unused energy sources.